The major objective of the proposed research is to collect data that will provide a foundation for a larger program of studies designed to investigate the development of social categorization in human and nonhuman primate infants. The work proposed addresses the effect of social and cognitive variables of the stimulus on the categorization of gender in socially experienced juvenile pigtail macaques (Macaca nemestrina). An operant procedure similar to that used previously in concept studies with monkeys will be used to investigate three specific questions: (1) the degree to which macaque subjects will acquire and generalize a social concept, in this case gender, (2) the degree to which the amount of information provided in the stimulus affects generalization of the discrimination, and (3) the degree to which the age of the stimulus affects generalization of the discrimination. The data obtained in the proposed research will provide an empirical foundation for future studies of social categorization and face perception in human and nonhuman primate infants, which will lead to a theoretical understanding of the development of social perception in primate infants.